The mobile crane crashed into the woman's two-storey home on Pendle Way in Pendle Hill about 5.30pm, Fire and Rescue NSW said. An entire wall and a large part of the red tile roof collapsed.

The woman was at the rear of the house at the time of the crash.

The driver of the 20-tonne crane escaped with a cut on his head and has been taken to hospital. Paramedics treated the woman for shock at the scene. She remains at her property.

Police said they were investigating.

"We don't know yet whether the brakes have failed, whether it was driver error or something mechanical. We're not sure," a police spokesman said.

At 7pm, Fire and Rescue said 15 crew members were at the scene working to "stabilise" the house.

"We've deployed our search and rescue vehicles, and they will shore up the house prior to getting the crane out," a Fire and Rescue spokesman said.